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from django.db import models
from django.utils.translation import ugettext_lazy as _
from django.utils.encoding import smart_unicode
class ContentTypeManager(models.Manager):
# Cache to avoid re-looking up ContentType objects all over the place.
# This cache is shared by all the get_for_* methods.
_cache = {}
def get_for_model(self, model):
"""
Returns the ContentType object for a given model, creating the
ContentType if necessary. Lookups are cached so that subsequent lookups
for the same model don't hit the database.
"""
opts = model._meta
key = (opts.app_label, opts.object_name.lower())
try:
ct = self.__class__._cache[key]
except KeyError:
# Load or create the ContentType entry. The smart_unicode() is
# needed around opts.verbose_name_raw because name_raw might be a
# django.utils.functional.__proxy__ object.
ct, created = self.get_or_create(
app_label = opts.app_label,
model = opts.object_name.lower(),
defaults = {'name': smart_unicode(opts.verbose_name_raw)},
)
self._add_to_cache(ct)
return ct
def get_for_id(self, id):
"""
Lookup a ContentType by ID. Uses the same shared cache as get_for_model
(though ContentTypes are obviously not created on-the-fly by get_by_id).
"""
try:
ct = self.__class__._cache[id]
except KeyError:
# This could raise a DoesNotExist; that's correct behavior and will
# make sure that only correct ctypes get stored in the cache dict.
ct = self.get(pk=id)
self._add_to_cache(ct)
return ct
def clear_cache(self):
"""
Clear out the content-type cache. This needs to happen during database
flushes to prevent caching of "stale" content type IDs (see
django.contrib.contenttypes.management.update_contenttypes for where
this gets called).
"""
self.__class__._cache.clear()
def _add_to_cache(self, ct):
"""Insert a ContentType into the cache."""
model = ct.model_class()
key = (model._meta.app_label, model._meta.object_name.lower())
self.__class__._cache[key] = ct
self.__class__._cache[ct.id] = ct
class ContentType(models.Model):
name = models.CharField(max_length=100)
app_label = models.CharField(max_length=100)
model = models.CharField(_('python model class name'), max_length=100)
objects = ContentTypeManager()
class Meta:
verbose_name = _('content type')
verbose_name_plural = _('content types')
db_table = 'django_content_type'
ordering = ('name',)
unique_together = (('app_label', 'model'),)
def __unicode__(self):
return self.name
def model_class(self):
"Returns the Python model class for this type of content."
from django.db import models
return models.get_model(self.app_label, self.model)
def get_object_for_this_type(self, **kwargs):
"""
Returns an object of this type for the keyword arguments given.
Basically, this is a proxy around this object_type's get_object() model
method. The ObjectNotExist exception, if thrown, will not be caught,
so code that calls this method should catch it.
"""
return self.model_class()._default_manager.get(**kwargs)
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